Updates on Technique
Can we deliver the same results safely with a cannula as we historically have with needles?
The question whether a cannula or a needle should be chosen for dermal filler injections does not have a straightforward answer. Injection techniques and location, as well as cannulas and needles have to be used in a patient specific manner. Over the last 5 years, practitioners have been adopting the use of cannulas for injection of dermal fillers. However, there is new literature supporting the safety and efficacy of cannula use with dermal fillers.
- PRECISION: With a sharp needle, placement of the needle tip is considered very precise especially when placing supraperiosteal
- LEARNING CURVE: easier for clinicians who are already using needles to inject other substances
- TRAUMATIC: increased risk of bruising and vascular events
In theory, the use of needles results in increased precision of injection. We are able to target and deliver the injected substance into the desired anatomic planes. However, there may be risk of spread if the substance tracks upward with the perpendicular movement of the needle. Cannulas are long and inserted at an oblique angle, theoretically confining the material into the desired plane of injection. However, using a longer needle may minimize retrograde migration along the trajectory of the needle path.
- The blunt tip may act to displace blood vessels rather than lacerate them
- Decrease risk of bruising, edema, and pain
- Decrease risk of inadvertent injection into a blood vessel resulting in a vascular event
- Long length allows for greater coverage through less injection points
- Decreased pain with procedure
- Decreased risk of bruising
- The blunt tip may act to displace blood vessels rather than lacerate them
Although cannulas may be more comfortable for patients, the sensation of the cannula moving through tissue may be disconcerting. There is an increased chance of vasovagal reaction. This can be perturbed by discussing with the patient what to expect and having an open dialogue during the procedure.
In a recent study evaluating the efficacy of needle vs. cannula for dorsal hand rejuvenation, there was comparable improvement between both techniques. However, there was 12% greater patient satisfaction with the cannula technique (PMID: 32976172).
In terms of efficacy, both needle and cannula deliver comparable aesthetic results. It has been suggested that the use of blunt microcannulas increases volume efficiency and decreases treatment time. However, optimal placement and results ultimately depend upon the knowledge and skill of the injector. With proficient use of cannula, practitioners can deliver similar aesthetic results.
Currently, these are the FDA approved indications for cannula use in USA:
- Restylane Silk – Lips – 2017
- Restylane Lyft – Cheeks – 2018
- Juvederm Voluma – Cheeks – 2019
- Juvederm Voluma – Chin/Prejowel sulcus – 2020
- Restylane Contour – Cheeks – 2021
And more to come!
Why adopt a new and initially more difficult technique? Minimizing the rare catastrophic events of needle injection, necrosis and blindness, is a major reason to consider use of cannula.
However, are cannulas really safer?
In a recent retrospective cohort study cohort study of 370 participating dermatologists, the risk of vascular occlusion appeared exceedingly low (1 in 6410 syringes via needle and 1 in 40,882 via microcannula injector) when board-certified dermatologists used needles or cannulas for filler injection (PMID: 33377939).
The blunt tip of a cannula is thought to laterally displace vessels preventing vascular penetration. However, the risk of inadvertent vascular injection is not completely eliminated with cannula use. There is greater force required to pierce a vessel with cannula compared to needle.
In a study comparing the arterial wall penetration forces in needles versus cannulas, it was shown that when using a 27-gauge needle or cannula, an artery could be penetrated with a similar force independent of whether the injector was utilizing a needle vs. cannula (PMID: 30589824).
Forces needed to penetrate vessels significantly decreased with smaller diameter cannulas. Cannulas require greater forces for intraarterial penetration compared with correspondingly sized needles, confirming the safety of larger diameter cannulas such as 22-gauge cannulas. Therefore, the more narrow the microcannula, the more potential to cause neurovascular injury or even to penetrate a blood vessel if passed through tissue with inappropriate force.
Injection force may be related to cannula shape as well. More fine-tipped cannulas are easier to use and move through tissue planes, however, it is also associated with increased risk for inadvertent arterial injection. Cannula location and direction matters as well. Large cannulas can tear the arterial wall if the artery wall is relatively fixed, for example against bone or from scar tissue after surgery. It is proposed that the artery cannot be displaced and is unable to avoid injury. Arterial location perpendicular to the cannula trajectory carries the most risk, especially if the artery is fixed.
Updates on Injection Force
Historically, it was been thought that slow and steady injection of filler may reduce the risk of vascular events. There has been great emphasis on the injection force; the pressure applied by the practitioner’s thumb on the syringe plunger. However, the ejection force of the filler leaving the needle or cannula lumen is very important. Irrespective of the injection force applied, if the ejection pressure exerted by a filler injection is higher than the arterial pressure, that ejection force may result in a vascular event (PMID: 33713373). Thus, knowing your anatomy and using the appropriate tools will be most helpful in preventing adverse events.
Updates on Dermal Fillers and Neuromodulators
Lower face injections are a highly requested area for rejuvenation. Patients are requesting neuromodulators and dermal filler injections to restore a youthful and more attractive lower facial contour.
Age related changes of the lower face:
- Loss of mandibular height and length
- Chin retrusion
- Exaggerate prejowel sulcus
- Increase in submandibular adipose
For lower face injections, we strive to create the appropriate shape and contour by maximizing the effects of lights and shadows. For the jawline definition, we want to create a shadow underneath jawline and chin in order to create balanced projection with the upper face.
Mandibular Width and Length
Neuromodulators can be used to treat aesthetic and functional changes of the lower face. For aesthetic purposes in women, decreased mandibular width can be achieved with neuromodulators in the masseter muscle. This can also be used for functional treatment of bruxism in men or women.
Dermal fillers can be used to add width by injecting deep at the mandibular angle. Soft tissue fillers with a high G prime should be used. These fillers have increased resistance to movement and decreased spread after placement resulting in increased volume support after injection.
To add length to the mandible, dermal fillers can be injected supraperiosteal along the angle of the mandible, with a focus on the pre-jowel and post-jowel sulcus.
Restylane Defyne has been approved by the FDA for augmentation and correction of mild to moderate chin retrusion for adults over the age of 21. Dermal fillers can be injected into the mentum inferiorly to elongate the face or anteriorly to aid in chin projection.
In men, the median point on the anterior surface of the chin should project approximately as far as the lower lip. The chin width should span the oral commissures. Whereas in women, the lower lip should project 1-2 mm beyond the chin and the chin should span the medial canthi. A tapered supraperiosteal injection pattern will result in a more feminine aesthetic. Neuromodulators can also be used to enhance the appearance of the chin. Neuromodulator injection into the mentalis muscle will relax the mentalis muscle allowing for inferior displacement of the chin.
Take home points:
- Both cannula and needle deliver similar aesthetic outcomes
- The use of needles allows for more precise injections.
- Can treat a large area from a single insertion point
- Have less risk of occlusion
- There are 3 things to consider in terms of cannula safety: size, shape and direction
- Lower face rejuvenation is highly requested area of treatment especially chin augmentation
This information was presented by Dr. Terrence Keaney at the 2022 ODAC Dermatology, Aesthetic and Surgical Conference held January 14-17, 2022. The above highlights from his lecture were written and compiled by Dr. Mojgan Hosseinipour.
Did you enjoy this article? Find more on Aesthetic Dermatology here.